An electrophotographic photoreceptor essentially comprises a charge generation layer (CGL) and charge transport layer (CTL) coated on a suitable substrate. The substrate may be an aluminized MYLAR polyester or an anodized aluminum drum. An aluminum drum can be coated with a suitable sub-layer and/or a barrier layer, derived by dispersing metal oxides in a polymer binder.
The charge generation layer comprises pigments or dyes selected from phthalocyanines, squaraines, azo compounds, perylenes, etc. The pigment or dye may be dispersed or dissolved in a suitable solvent, with or without a polymer binder.
The charge transport layer comprises a charge transport material or multiple charge transport materials in a polymer binder matrix. Additives such as fluoropolymers or inorganic oxides may also be used. An overcoat layer comprising only a polymer layer or a charge transport material-polymer composite may also be used. Typically, the charge transport layer is the outer layer and is subject to wear from movement in contact with other items such as rollers, doctor blades and the toner. An area of active interest is to increase the life of the photoconductor drum or member.
There are several approaches that have been used to achieve increased life. Incorporation of lubricants or inorganic oxides is known to help lower wear or abrasion. These lubricants can be polysiloxanes or silicone oils, or fluoropolymers, and the inorganic materials may be silica, titania, etc. The use of lubricants such as silicone oils is easy to implement. However, it is difficult to constantly lubricate the surface, as the silicone oil may be removed on contact with paper or toner. High concentrations of silicone oil can result in poor coating quality and result in coating defects that eventually translate to print defects. Excess silicone oil can also be detrimental to print performance.
Other methods involve the use of materials that are capable of undergoing cross-linking reactions in the outer layer of the photoconductor member. Cross-linking reactions may be brought about by either chemical reactions or subjecting the cross-linkable materials to photoradiation. The use of catalysts to promote the chemical reaction leading to cross-linking will require the material to be inert to the electrophotographic process. Most catalysts are ionic, acidic or alkaline. Non-inert catalysts, although used in small amounts, can have a significant impact on the electrostatics of the photoconductor member. Use of photoradiation may result in cross-linking reactions only at the surface layers, possibly a few microns in thickness and not in the bulk.
Hence, there is a need to experiment and formulate systems that impart good wear characteristics.